JPS60142375A - Double-sided image forming device - Google Patents

Abstract

PURPOSE:To prevent a sheet from curling and wrinkling during the fixation of the 1st surface, and save energy by making the degree of the 1st and the 2nd surfaces lower in both-surface image formation than in one-surface image formation. CONSTITUTION:A heating source 53 is provided with a main heating body 53a and an auxiliary heating body 53b, which are both powered on during the fixation of one-surface copying operation. When a both-surface copy is taken, the auxiliary heating body 53b is powered off with the signal for the start of both- surface copying operation and only the main heating body 53a is powered on. The set surface temperature of a fixing roller 51 is controlled to 190 deg.C in one- surface copying operation or to 170 deg.C in the both-surface copying operation by varying the detection level of a thermistor. Consequently, the heating value applied to the sheet is reduced in the both-surface copying operation to decrease the degree of fixation.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a double-sided image forming apparatus such as a copying machine that forms images. In particular, the present invention relates to a double-sided image forming apparatus with an improved fixing device for fixing a toner image on a sheet.

Conventionally, various copying machines have already been proposed and realized for performing so-called double-sided copying, in which copy images are formed on both the front and back sides of a sheet using electrophotography. For example, one side of a sheet (one side) is used for normal one-sided copying, the sheet in the single-sided copy tube is guided again to the original paper feed section, or another second paper feed section, and then the other side of the sheet is copied again. There is a type that sends the paper to a processing section and copies it on the back side in the same way as the front side.This is the most popular because only one set of copying processing section is required and the structure is simple and compact. This is a practical double-sided copying machine.In this type of double-sided copying machine, the fixing device for fixing the image on the sheet is a heat-fixing device that fixes the image by passing the sheet between a pair of rollers that are heated and pressed together. A roller fixing device is used as it is highly efficient.The factors that affect the degree of fixing in this hot roller fixing device are 7"
, t, and the nip amount is a function of the width of the nip caused by the pressing force of the roller, the amount of heating, and the moving speed of the sheet, and determines the degree of fixing.

By the way, in conventional double-sided copying machines, not only is the nip amount the same for single-sided copying and for fixing the first side and the second side of double-sided copying, but also the pressure contact force, which is an element thereof, is
The amount of heating and the speed of movement are also done in exactly the same manner. However, the state of the sheet to be fixed differs greatly between the first fixing and the second fixing. In other words, some of the moisture normally contained in the sheet has been removed after the first side has been completely fixed, and furthermore, the sheet has residual heat after the first side has been fixed.

In addition, if the first side is fixed at a high fixation rate, wrinkles and curls tend to occur on the sheet.
This may interfere with subsequent processes such as surface image transfer. Therefore, it is not necessarily a good idea to perform fixing with the same amount of Nizzo for single-sided copying and double-sided copying, as has been the case in the past.

SUMMARY OF THE INVENTION An object of the present invention is to provide a double-sided image forming apparatus equipped with a heat roll fixing device that can prevent sheet curls and wrinkles caused by the first fixing process and save energy.

The gist of the present invention is to provide double-sided imaging having a common heated roller fuser for fixing a toner image formed on a first side of a sheet and then fixing a toner image formed on a second side of a sheet. A double-sided image forming apparatus is characterized in that the degree of fixation on the first side and the second side in the case of double-sided image formation is lower than the degree of fixation in the case of single-sided image formation.

FIG. 1 is a side sectional view of a double-sided copying machine according to an embodiment of the present invention.

In the figure, an original 1 is placed on a transparent plate 2 of an original table, and the optical system is composed of a moving reflection mirror 3.4, a lens 5, and a fixed reflection mirror 6.7.

That is, the original 1 is moved by a movable reflection mirror 3 that moves together with the illumination lamp 8, and a movable reflection mirror 4 that moves in the same direction at the moving speed of its rod of the movable reflection mirror 3.
The optical path length is kept the same by the Nakara, and the light passes through the lens 5 and the fixed reflection mirror 6.7, and is exposed to the slit, and is deposited on the photosensitive drum 9 (g-J). Here, the surface of the photosensitive drum 9 is covered with the photoconductive layer Consists of a photoreceptor covered with a transparent insulating layer,
As the photoreceptor rotates, it is first positively charged by a glass charger 11 to which a high positive voltage is supplied from a high voltage power supply 10. Subsequently, when reaching the exposure section 12, the illumination run f
The image of the original 1 on the transparent plate 2 of the original table illuminated at
An image is formed on the drum 9 by this. The photosensitive drum 9 receives an AC corona discharge from an AC corona discharger 13 to which an AC high voltage is supplied from a high voltage power supply 10 at the same time as the original image is exposed to the photosensitive drum 9 . Next, the photoreceptor is fully exposed by the entire surface exposure lens 14 to form an electrostatic latent image on the surface of the photoreceptor drum 9, which then reaches the developing device 15. Development is performed by powder development using a magnetic sleeve method, and the electrostatic latent image is visualized. On the other hand, sheets are sent out from the paper feed section, and the relay tray 17 and first paper feed table 18 of the paper feed section
is a cassette type, and the second paper feed tray 19 is a deck type having an automatic paper elevating device and capable of stacking a relatively large number of sheets, and the relay tray 17 is also used as a paper feed tray during double-sided copying. The first side of the sheet sent from one of the paper feed sections 17, 18, and 19 is brought into close contact with the drum 9. Therefore, the transfer charger 20 positively charges the sheet using the high-voltage power supply 10, and transfers the image on the drum 9 onto the sheet. After the transfer, the sheet is transferred to the drum 9 at the separating section 21.
The paper is separated from the paper and guided to the fixing device 23 via the conveyance path 22.

The fixing device 23 includes a fixing roller 51 having a heat source 53.
and a pressure roller 52 having a rubber layer on its surface. A sheet having a powder image passes between these rollers that are in pressure contact with each other, and the powder image is fixed on the sheet by pressure and heat.

In the case of double-sided copying, the sheet that has passed through the fixing device 23 is sent to a conveyance path 27a, and further transferred to a relay tray 17.
It is stored with the image formed on the first surface facing up.

A set number of sheets are stacked in the relay tray 17 through a similar copying process.

When the next copy button (not shown) is turned on, the first side copied sheet in the relay tray 17 is sent to the conveyance path 46.
After the toner image on the photosensitive drum 9 is transferred to the second surface of the sheet, the sheet is discharged into the soak 30 or the tray 31 via the conveyance path 22, the fixing device 23, and the conveyance path 27b or 27c. The same copying process is then repeated for the set number of copies.

Note that in the case of only one-sided copying, the sheet that has passed through the fixing device 23 is guided to a conveyance path 27b or 27c, and is carried out into a sorter 30 or a tray 31. In this way, the conveyance path is normally located at the position 27e indicated by the solid line, and is switched to the position indicated by the dotted line 27a or 27b in response to a signal if necessary.

FIG. 2 shows a detailed diagram of the heat source 53 used in the fixing device 23 of the embodiment shown in FIG.

That is, the heat source 53 is provided with a main heating element 53a and an auxiliary heating element 53b, and during fixing in the case of only one-sided copying, the main heating element 53a and the auxiliary heating element 53b are also energized, but in the case of double-sided copying, In response to the signal to start duplex copying, the auxiliary heating element 53b is de-energized, and the main heating element 53a is turned off.
energized only. In this configuration, the set temperature of the surface of the fixing roller 51 for single-sided copying is controlled to be 190°C, and the set temperature for double-sided copying is controlled to be 170°C by changing the detection level of the thermistor. conduct. As a result, in the case of double-sided copying, the amount of heat applied to the sheet is reduced and the degree of fixation is lowered. Although such a temperature change is somewhat lacking in quick response, it is effective in saving power when producing a large number of double-sided saws.

3, 4, and 5 are cross-sectional views of a fixing device according to another embodiment of the present invention, in which the fixing device 2 shown in FIG.
This corresponds to 3. (The double-sided copying machine of this embodiment is generally the same as shown in FIG. 1 except for the fixing device.) In these figures, 51 is a fixing roller, which has a heat source 53 inside. ing. 52 is a pressure roller. A thermistor 55 for controlling the surface temperature is pressed against the surface of the fixing roller 51, and the thermistor 55 turns on and off the amount of heat 53.

An arm 57 supporting both ends of the pressure roller 52
is pivotally supported at one end and connected to one end of a lever 59 via a compression spring 58 at the other end, and this lever 59 is engaged with the pin 60' of a cam 60 at the other end, and the rotation of this cam 60 The spring 58 is provided so as to swing in the direction A-B in the figure about point b, thereby compressing and expanding the compression spring 58.

6 and 7 are surface elastic layers of the pressure roller.

When paper is not being passed, the lever 59 is not biased by the cam 60 as shown in FIG. 3, and the pressure roller 52 is separated from the fixing roller 51. On the other hand, during paper feeding, the lever 59 is biased and swung in the direction A by the rotation of the cam 60 by a motor (not shown), and the arm 57 is moved to the center point a of the axis ai by the spring force of the compression spring 58. By rotating as follows, the pressure roller 52 is brought into pressure contact with the fixing roller 51.

Now, the fixing operation in such a fixing device will be described below. First, in the case of one-sided copying, the fixing roller 5 is activated by a drive motor (not shown) in response to a copy start signal.
1 and the pressure roller 52 start rotating, and the pressure motor (not shown) operates to rotate the cam 60, biasing the sillper 59 to the bin 60' and applying pressure as shown in FIG. The pressure roller 52 is brought into pressure contact with the fixing roller 51.

The recess 64 formed on the outer circumference of the cam 60
When a nearby sensor 61 detects this, the pressurizing motor and therefore the cam 60 are stopped, and the motor's own brake (depending on the mechanism, the pair of rollers 51.5) is stopped.
2 is locked so that the pressurized state is maintained. This state is shown in FIG.

The stopping position of the cam 60 is set at the position shown in FIG.
It is preferable to set it in the free escape position. Due to the movement of the lever 59, the arm 57 receives the force of the compression spring 58 to bring the pressure roller 52 into pressure contact with the fixing roller 51, and these rollers rotate in a state of pressure contact. A sheet having an unfixed image is fixed by passing between the rollers.

As in the case of single-sided copying as described above, the fixing operation at the stop position when the sensor 61 detects the four portions 64 is referred to as first position fixing.

Normally, when one-sided copying is completed, the copy sheet is transferred to the path 2f.
7; c or 27'b, and is discharged outside the machine, and in response to a signal indicating completion of discharge outside the machine, rotation of the roller 52 is stopped and the brake of the pressurizing motor that drives the cam 60 is released. At this time, as described above, the cam 60 is in contact with the lever 59 in a free-running state, so when the brake of the motor is released, the repulsive force of the spring 58 and the weight of the roller 52 cause the cam 60 to reach a stable contact position with the lever 59. (the position shown in FIG. 3).

Next, in the case of double-sided copying, the rotation of the roller pair and the rotation of the cam 6o are started by the copy start signal, as in the case of FIG. 4, but in this case, as shown in FIG. When the sensor 61 provided nearby detects another four part 63 formed on the outer circumference of the cam 6o, the cam 6o is stopped and locked at this position by the brake mechanism described above, and the corresponding application is performed. Roller 51 in pressure state
°52 is maintained. In the case of double-sided copying, the sheet is fixed by passing between the pair of rollers under pressure. This state is shown in FIG.

The fixing operation at the stop position when the sensor 61 detects the recess 63 as in the case of double-sided copying as described above is referred to as second position fixing.

The recess 63 is located downstream of the recess 64 when viewed in the drive rotation direction (arrow) of the cam 60. In the case of double-sided copying, the cam 60 is driven by a pressure motor (not shown) and rotates in the direction of the arrow, and the first concave portion, that is, the four portions 63
When the rotation is detected, the rotation is stopped and locked, and when the copying is completed, the brake of the pressurizing motor is released as described above, and the repulsive force of the spring '58 and the pattern needle of the roller 52 cause the motor to return to the stable contact position with the lever 59. It is made to rotate. In the case of single-sided copying, when the sensor 61 detects the second recess, that is, the recess 64, the rotation is stopped and the pressure is released.

As is clear from Figures 4 and 5 and the above explanation, the roller pressure contact force is different between the fixing at the first position and the fixing at the second position. It has become. It is known that the factor that determines the degree of fixing is called the nip amount, and the nip amount is expressed by time x heating amount x nip width. In this embodiment, since the pressurizing force is large in fixing at the first position, the degree of fixing is higher than that at the second position when D=nip is dog. That is, in double-sided copying, the degree of fixing is lower than in single-sided copying.

FIG. 6 is a flowchart showing the roller pressing operation of this embodiment.

The above-mentioned embodiment in which the degree of fixing is lowered in double-sided copying than in single-sided copying by changing the pressing force of the pair of rollers is an embodiment in which the degree of fixing is changed by changing the temperature described above. ) Excellent responsiveness.

In addition to the two embodiments of the present invention described above, in the present invention, in order to make the degree of fixation lower in double-sided copying than in single-sided copying, only the roller setting temperature or the roller pressure is required. In addition to changing the temperature, the temperature and pressure are gradually lowered for double-sided copying compared to single-sided copying.

According to the present invention described above, it is possible to obtain a rational double-sided image forming apparatus that realizes power saving and long life.

[Brief explanation of the drawing]

FIG. 1 is a side sectional view of a double-sided copying machine according to an embodiment of the present invention, FIG. 2 is a diagram of a fixing roller heating source of the same embodiment, and FIGS. 3, 4, and 5 are FIG. 6 is a sectional view showing different operating states of a fixing device according to another embodiment, and FIG. 6 is a flowchart showing pressurizing and releasing operations of the fixing device. 9... Photosensitive drum, 17... Relay tray, 18.
19...Paper feed tray, 23...Fixing device, 30...
Sorter, 31... Paper discharge tray, 51... Fixing roller, 52... Pressure roller, 53... Heat source,
55... Thermister, 57... Arm, 58-...
・Compression spring, 59... Lever, 60... Cam, 6
1...sensor, 63.64...recess. Figure 5

Claims (1)

[Claims] In a double-sided image forming apparatus that has a common heat roller fixing device that fixes the toner image formed on the first side of the sheet and then fixes the toner image formed on the second side of the sheet, A double-sided image forming apparatus characterized in that the degree of fixation on the first side and the second side in the case of image formation is lower than the degree of fixation in the case of single-sided image formation.